1. Field of the Invention
The present invention relates to a land grid array (LGA) connector assembly which comprises an LGA connector and a pick-up cap mounted on the LGA connector for providing a plane surface to be engaged by a vacuum suction device, whereby the LGA connector assembly can be moved onto a circuit substrate such as a printed circuit board (PCB) on which the LGA connector is to be mounted.
2. Description of the Prior Art
On many production lines, electronic components such as land grid array (LGA) connectors are accurately positioned on circuit substrates such as printed circuit boards (PCBs) by means of vacuum suction devices.
A method of mounting the electrical connector onto the PCB by SMT generally comprises a sequence of the following steps A through F:    A—Application of an adhesive film on the PCB having a plurality of metal contact pads. The application of the adhesive film may be performed by screen printing, pin transfer, or from a dispenser onto predetermined areas of the PCB.    B—Activation of the adhesive film by irradiation with actinic light in the ultraviolet (UV) or visible wavelength ranges between 200 and 600 nm, to a degree and for a period of time such that a desired initial tackiness is produced.    C—Mounting the connector with its contacts on the activated adhesive film and the metal contact pads of the PCB.    D—Curing the adhesive film at a temperature between 60˜140° C.; for example, in a convection cabinet, using infrared radiant heaters or by means of the actinic radiation source used in step B if such source also produces infrared radiation.    E—Producing electrical engagement between the contacts of the connector and the corresponding metal contact pads of the PCB by soldering in a wave solder machine or in drag soldering equipment.    F—Cooling the assembly to room temperature.
In step C, the connector is accurately positioned on the PCB by a vacuum suction device. Generally, a typical connector has a plurality of holes in a flat top portion thereof. Thus the connector does not have a suitably smooth, integral top surface for engagement by a vacuum suction device. Typically, a pick-up cap is attached on the top portion of the connector to provide a required plane top surface.
Referring to FIG. 5, such a conventional LGA connector 8 typically comprises an insulative housing 80, a plurality of electrical contacts (not labeled) received in corresponding passageways (not labeled) of the housing 80, a metal stiffener 81 partly covered and reinforced the housing 80, a metal clip 82 pivotably mounted to an end of the housing 80, and a lever 83 pivotably mounted to an opposite end of the housing 80 for engaging with the clip 82. The clip 82 has a generally rectangular window (not labeled) in a middle portion thereof. Each contact has a contact portion protruding outwardly from an upper surface of the housing 80, for electrically connecting with a corresponding metal contact pad of an electronic package such as an LGA central processing unit (CPU) that is received in the LGA connector 8. Because of this configuration of the LGA connector 8, a pick-up cap 9 has to be pre-attached on a top portion of the housing 80 and sheltered almost all the passageways to prevent dirty material from falling onto the contacts. The pick-up cap 9 has a generally rectangular body 90. Typically, a plurality of latches 91 depends perpendicularly from sides of the body 90. The latches 91 snappingly engage with corresponding sidewalls of the clip 82, thereby mounting the pick-up cap 9 onto the LGA connector 8. The pick-up cap 9 has a plane top surface exposed through the window of the clip 82. A vacuum suction device (not shown) can accordingly engage on the top surface of the pick-up cap 9, in order to reliably move the LGA connector 8 and accurately position it onto the PCB.
When curing the adhesive film at high temperature in a convention cabinet using infrared radiant heaters, heat air can only flow through a few of the passageways which are not sheltered by the pick-up cap 9 to a bottom portion of the housing 80. Generally, the time needed for curing the adhesive film is short. Thus, the adhesive film is liable to cure non-uniformly. When this happens, electrical engagement between some of the contacts and the corresponding metal contact pads of the PCB may be flawed. The connector 8 may not reliably electrically connect with the PCB. Additionally, when cooling the entire assembly to room temperature, heat air can only be dissipated out through the passageways that are not sheltered by the pick-up cap 9. This increase the time need for cooling the assembly, which reduces the efficiency of mounting the connector 8 onto the PCB.
Referring to FIG. 6, to solve the above-mentioned problem, another pick-up cap 9′ is provided. The pick-up cap 9′ has generally rectangular vents 900′ extending through the planar body 90′ in a vertical direction thereof. When curing the adhesive film at high temperature in a convention cabinet using infrared radiant heaters, heated air can flow through the vents 900′ and get to a bottom of the connector 8′ to make the adhesive film of the contacts activated quickly. Therefore, the connector 8′ can be reliably and electrically soldered onto the PCB in a short time, and the efficiency of mounting of the connector 8′ onto the PCB is improved. However, a new problem appears. Because of the vents 900′ in the pick-up cap 9′, when heated air flow through the vents 900′ into the bottom of the connector 8′, heated air will be held up by corresponding inner walls of the vents 900′ so that heated air can not uniformly flow into the connector 8′, which makes the adhesive film of the contacts adjacent to the vents 900′ activated quickly while the adhesive film of the contacts away from the vents 900′ activated slowly. Thus the connector 8′ may not reliably and electrically connect with the PCB in time.
Thus, there is a need to provide a new electrical connector assembly with a pick-up cap that overcomes the above-mentioned problems.